For input devices used in mobile apparatuses in which portability is considered important and in mobile apparatuses in which a display unit such as a display is considered important, there have been desired input devices with small input unit on the apparatuses.
As a method for reducing a key layout space of the input unit on the apparatus, there is considered a method which allots a plurality of functions to a single input. As an example thereof, there is a method which places a joystick on the apparatus for detecting tilt angles in the top-and-bottom and right-and-left directions, and switches characters according to the tilt directions (e.g., see Patent Document 1). However, the tilt directions of the joystick of this method used for inputting each character is different from a widely-used mobile apparatus input method, so that it is required to be accustomed thereto for the input. Since input operations become complicated, input errors may be induced.
Further, there is also a method with which a detecting unit is separated from the apparatus and placed independently. As an example thereof, there is a device with which input is done by having a detecting unit attached to the body (e.g., see Patent Document 2). However, with this method, it is necessary to prepare an input unit separately from the apparatus, and it is not excellent in terms of portability. Further, it is a troublesome work to attach the detecting unit to an operator.
Furthermore, as a method for reducing the space of the input unit for detecting actions to the surface of the apparatus, there is a method which inputs characters with handwriting through detecting digital compressions in X-, Y-, and Z-axis directions. As a conventional example thereof, there is a method which uses a track point, and inputs characters with handwriting from the digital compression changing pattern (e.g., see Patent Document 3) However, it is difficult to check the action since there is no movement in the fingertip that conducts the input action, and it may cause input errors.    Patent Document 1: Japanese Unexamined Patent Publication 2005-258734    Patent Document 2: Japanese Patent Application Publication 2004-537802    Patent Document 3: Japanese Unexamined Patent Publication 2005-301874